The present invention is directed to an output voltage detecting device in a laser oscillator, and more particularly to an output voltage detecting device in a laser oscillator which is operable at a low voltage and manufactured at an inexpensive cost.
A laser tube has an electrical impedance which varies depending upon an confined gas status in the interior of the laser tube. As a consequence, a voltage supplied to the laser tube varies. For example, in a laser oscillator having a current feedback loop with which a current is fedback to the laser tube, the variation in the electrical impedance of the laser tube causes the supply voltage to vary, since the current is being controlled to be a constant. If this condition is left as it stands, semiconductor elements, the laser tube or other elements which form an inverter in a high frequency power supply are damaged. Furthermore, the output voltage needs to be monitored to ascertain if the supply voltage is stable.
In view of the foregoing, it is conventional practice to detect the voltage supplied to the laser tube, and when the resultant voltage is above a reference voltage, an alarm is generated. When the detected voltage is above a danger-level voltage, the driving is stopped. In addition, it has been necessary to detect and monitor the output voltage in order to control the output voltage to a constant. Accordingly, it can be appreciated that in the laser oscillator, monitoring of the voltage supplied to the laser tube and measurement thereof are important measuring items. Conventionally, such measurements have been carried out using a transformer or voltage-division capacitors.
However, the transformer is required to have a considerably high voltage insulation resistivity. The transformer is further required to have a high frequency characteristic attendant to the high frequency power supply unit. For such reasons, the transformers which are extremely expensive have to be employed.
A method in which the voltage is divided by capacitors is involved with a problem such that a power supply line led to the laser tube cannot be isolated from a ground connection of a control apparatus, so that noise is liable to be introduced into a control circuit.